For now, I will let Michael Walzer answer that question. Walzer is professor emeritus at the Institute for Advanced Study (IAS) in Princeton, New Jersey. He is also the co-editor or the leftist magazine Dissent.
In this clip, Walzer talks about the history of just war theory. He also addresses elements of his own thought on the matter. In the post-Vietnam-era, few have done more to advance just war theory than Michael Walzer.
Talk a listen:
(Source: Big Think)
For Walzer’s full treatment of just war theory, check out his classic treatise Just And Unjust Wars: A Moral Argument With Historical Illustrations.